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drm/i915: Reduce nested prepare_remote_context() to a trylock

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On context retiring, we may invoke the kernel_context to unpin this
context. Elsewhere, we may use the kernel_context to modify this
context. This currently leads to an AB-BA lock inversion, so we need to
back-off from the contended lock, and repeat.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111732
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Fixes: a9877da2d6 ("drm/i915/oa: Reconfigure contexts on the fly")
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191126065521.2331017-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson 2019-11-26 06:55:21 +00:00
parent 5766a5ffc6
commit 58b4c1a07a
1 changed files with 17 additions and 4 deletions
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21
drivers/gpu/drm/i915/gt/intel_context.c
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@ -310,10 +310,23 @@ int intel_context_prepare_remote_request(struct intel_context *ce,
GEM_BUG_ON(rq->hw_context == ce);
if (rcu_access_pointer(rq->timeline) != tl) { /* timeline sharing! */
err = mutex_lock_interruptible_nested(&tl->mutex,
SINGLE_DEPTH_NESTING);
if (err)
return err;
/*
* Ideally, we just want to insert our foreign fence as
* a barrier into the remove context, such that this operation
* occurs after all current operations in that context, and
* all future operations must occur after this.
*
* Currently, the timeline->last_request tracking is guarded
* by its mutex and so we must obtain that to atomically
* insert our barrier. However, since we already hold our
* timeline->mutex, we must be careful against potential
* inversion if we are the kernel_context as the remote context
* will itself poke at the kernel_context when it needs to
* unpin. Ergo, if already locked, we drop both locks and
* try again (through the magic of userspace repeating EAGAIN).
*/
if (!mutex_trylock(&tl->mutex))
return -EAGAIN;
/* Queue this switch after current activity by this context. */
err = i915_active_fence_set(&tl->last_request, rq);